Working Machine and a Method for Operating a Working Machine

ABSTRACT

A working machine including an internal combustion engine for supplying torque to the driving wheels of the working machine, and a transmission line arranged between the internal combustion engine and the driving wheels for transmitting torque from the internal combustion engine to the driving wheels. The working machine further including at least one hydraulic pump in a hydraulic system for moving an implement arranged on the working machine and/or steering the working machine. The transmission line includes at least one electric machine for driving or braking the driving wheels, and/or for generating electric power for the at least one hydraulic pump.

BACKGROUND AND SUMMARY

The invention relates to a working machine and a method for operating aworking machine.

The invention is applicable on working machines within the field ofindustrial construction machines, in particular wheel loaders. Althoughthe invention will be described with respect to a wheel loader, theinvention is not restricted to this particular vehicle, but may also beused in other heavy working machines, such as articulated haulers,trucks and excavators.

A wheel loader is usually provided with an internal combustion engine, atransmission line, and a gearbox for supplying torque to the drivingwheels of the wheel loader. The gearbox provides different gear ratiosfor varying the speed of the vehicle, and for changing between forwardand backward driving direction. The transmission line comprises ahydrodynamic torque converter arranged between the internal combustionengine and the gearbox. The torque converter is used to increase thetorque during particularly heavy working operations, such as filling thebucket or acceleration of the wheel loader. The torque converter canvery quickly adapt the output torque to the current working conditions.However, the torque converter has often a very low efficiency which isalso dependent on the current driving conditions. The efficiency can beincreased if the torque converter is provided with a lock-up functionwhich can be used for direct operation. However, the gear ratio is fixed(1:1) in the lock-up state, and the problem of low efficiency remainsduring working operations where such a lock-up function cannot be used.

In addition to supply torque to the driving wheels, the internalcombustion engine has to supply energy to a hydraulic pump of ahydraulic system of the wheel loader. Such a hydraulic system is usedfor lifting operations and/or steering the wheel loader. Hydraulicworking cylinders are arranged for lifting and lowering a lifting armunit, on which a bucket or other type of attachment or working tool, forexample forks, is mounted. By use of another hydraulic working cylinder,the bucket can also be tilted or pivoted. Further hydraulic cylindersknown as steering cylinders are arranged to turn the wheel loader bymeans of relative movement of a front and rear body part of the wheelloader.

On one hand, the rotation speed of the internal combustion engine has tobe adapted to the hydraulic pump, and on the other hand, the internalcombustion engine has to be adapted to the need for a very high torque,for example during filling the bucket when the speed of the wheel loaderis close to zero. A rotation speed of the internal combustion enginedetermined by the hydraulic system means that the wheel loader has to bebraked so as to adapt the velocity of the wheel loader to the currentconditions. In order to fulfil the demands on speed of rotation andtorque in different situations, the internal combustion engine has to bedimensioned for an unnecessary high effective output which output is notrequired or is only infrequently required. The use of an internalcombustion engine which in some respects is oversized and further has tobe driven during circumstances where the torque converter has lowefficiency, and/or during conditions where the wheel loader has to bebraked due to the hydraulic system, will result in high fuelconsumption.

It is desirable that the invention is to provide a working machine ofthe kind referred to in the introduction, which working machine enablesa more effective operation of the working machine and lower fuelconsumption.

By the provision of a transmission line comprising an electric machinefor driving or braking the driving wheels, and/or for generatingelectric power for the hydraulic pump, the internal combustion enginecan be more efficiently used, which enables a smaller internalcombustion engine to be used, and the fuel consumption can be lowered.For example, the hydraulic system can be driven at least partly by theelectric machine instead of the internal combustion engine. Thus, therotation speed of the internal combustion engine does not need to bedetermined taking the hydraulic pump into consideration. The electricmachine can be used as a brake during a braking operation of the wheelloader, and at the same time function as a generator for recuperatingenergy. The energy can be directly supplied to the hydraulic system orstored in an electric energy storage means, such as a battery or supercapacitor, to be used later on. If a great traction force is required,an additionally torque can be supplied to the driving wheels by means ofthe electric machine functioning as a electric motor, and, thus the needof the torque converter is decreased.

Furthermore, the electric machine can be used for driving the drivingwheels in the reversed direction. This means that the reverse gear ofthe gearbox can be eliminated. A further advantage is that the electricmachine can be used for adapting the speed of rotation of the internalcombustion engine and the speed of rotation of the transmission line toeach other so as to facilitate coupling or decoupling of a directoperation state of a transmission unit comprised in the transmissionline.

By such a method the size and operation of the internal combustionengine can be optimized so as to keep the fuel consumption as low aspossible.

Further advantages and advantageous features of the invention aredisclosed in the following description.

By the term “electric machine” is meant a combined electric motor andgenerator. The electric machine can be driven by electricity to supplyan output torque on a shaft or be mechanically driven by applying torqueon a shaft for producing electricity.

The term “transmission unit” comprises hydraulic clutches, bothhydrodynamic clutches such as torque converters and hydrostaticclutches, as well as mechanical clutches. Thus, “transmission unit”comprises both torque converters which can increase the torque, andordinary clutches only used for disengagement and direct operation withthe gear ratio of 1:1.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detaileddescription of embodiments of the invention cited as examples.

In the drawings:

FIG. 1 is a lateral view illustrating a wheel loader having a bucket forloading operations, and a hydraulic system for operating the bucket andsteering the wheel loader,

FIG. 2 is a schematic illustration of a hydraulic system for a wheelloader,

FIG. 3 is a schematic illustration of a transmission line of a wheelloader according to prior art,

FIG. 4 is a schematic illustration of a transmission line of a workingmachine according to the invention, and

FIG. 5 is a schematic illustration of a variant of a transmission lineof a working machine according to the invention.

DETAILED DESCRIPTION

FIG. 1 is an illustration of a wheel loader 1 having an implement 2 inthe form of a bucket 3. The bucket 3 is arranged on an arm unit 4 forlifting and lowering the bucket 3, and further the bucket 3 can betilted or pivoted relative to the arm unit 4. The wheel loader 1 isprovided with a hydraulic system comprising at least one hydraulic pump(not shown in FIG. 1) and working cylinders 5 a, 5 b, 6 for theoperation of the arm unit 4 and the bucket 3. Furthermore, the hydraulicsystem comprises working cylinders 7 a, 7 b for turning the wheel loaderby means of relative movement of a front body 8 and a rear body 9. Aschematic illustration of such a hydraulic system is shown in FIG. 2. Inthe embodiment illustrated in FIG. 2, two working cylinders known aslifting cylinders 5 a, 5 b are arranged for lifting and lowering the armunit 4, and a further working cylinder known as tilting cylinder 6 isarranged for tilting-in or tilting-out the bucket 3 relative to the armunit 4. In addition, two working cylinders known as the steeringcylinders 7 a, 7 b are arranged for steering the wheel loader 1.Furthermore, three hydraulic pumps 100 a, 100 b, 100 c supply thehydraulic cylinders with hydraulic oil. An operator of the workingmachine can control the working cylinders by means of instrumentsconnected to a control unit (not shown).

FIG. 3 is a schematic illustration of a transmission line 11 of a wheelloader 1 according to prior art. At one end of the transmission line 11an internal combustion engine 12 is arranged. The other end of thetransmission line 11 is coupled to the driving wheels 13 of the wheelloader 1. The internal combustion engine 12 supplies torque to thedriving wheels 13 of the wheel loader 1 via the transmission line 11. Asillustrated, the transmission line 11 may comprise a gearbox 14 forvarying the speed of the vehicle 1, and for changing between forward andbackward driving direction of the wheel loader 1. A hydrodynamicconverter 15 is arranged between the internal combustion engine 12 andthe gearbox 14. The transmission line 11 of the wheel loader 1 has meansfor driving a hydraulic pump 10 in a hydraulic system for liftingoperations and steering the wheel loader 1. According to prior art thehydraulic pump 10 is driven by the internal combustion engine 12,preferably via gear wheels 16 arranged between the torque converter 15and the gearbox 14.

A transmission line 110 of a working machine 1 according to theinvention is schematically illustrated in FIG. 4. At one end of thetransmission line 110 an internal combustion engine 120 is arranged. Theother end of the transmission line 110 is coupled to the driving wheels130 of the working machine 1. The internal combustion engine 120supplies torque to the driving wheels 130 of the working machine 1 viathe transmission line 110. As illustrated, the transmission line 110 maycomprise a gearbox 140 for varying the speed of the vehicle 1, and forchanging between forward and backward driving direction of the workingmachine 1. In the embodiment illustrated in FIG. 4, the transmissionline 110 also comprises a transmission unit 150 for engagement anddisengagement of the internal combustion engine 120 relative to thedriving wheels 130. The transmission unit 150 is preferably a hydraulicclutch of the type called hydrodynamic torque converter. The torqueconverter is able to increase the torque, which means that the outputtorque of the torque converter can be for example in the interval 1-3times the torque of the internal combustion engine 120. Furthermore, thetorque converter has preferably a free wheel function and a lock-upfunction for direct operation without any increased torque. Thus, thetransmission ratio of the torque converter in the lock-up state isfixed, and preferably substantially 1:1 However, in an alternativeembodiment the transmission unit 150 could be an ordinary clutch fordisengagement or direct operation without any increased torque. Such aclutch could be a hydraulic clutch as well as a mechanical clutch.

According to the invention, the transmission line 110 of the workingmachine 1 comprises at least one electric machine 17 a, 17 b for drivingor braking the driving wheels 130, and/or for powering at least onehydraulic pump 100 a, 100 b, 100 c by electricity.

Although the embodiment illustrated in FIG. 4 has three hydraulic pumpsused for providing the functions described with reference to FIG. 2, inanother embodiment one, two, four or more hydraulic pumps may be used ina hydraulic system 20 for providing these functions and/or otherfunctions. In a preferred embodiment of the invention the workingmachine has at least two implement and/or steering functions, and atleast one said hydraulic pump is arranged for each implement and/orsteering function. In the embodiment examples schematically illustratedin FIGS. 2 and 4, the working machine comprises three hydraulic pumps100 a, 100 b, 100 c; a first hydraulic pump 100 a is arranged to providea lifting and lowering function of the implement, a second hydraulicpump 100 b is arranged to provide a tilting function of the implement,and a third hydraulic pump 100 c is arranged to provide the steeringfunction of the working machine. By separate hydraulic pumps for thesefunctions the operation of the working machine can be further optimizedand thus the total energy consumption can be lowered.

The electric machines 17 a, 17 b are electrically connected to thehydraulic pumps 100 a, 100 b, 100 c which has a respective motor 18 a,18 b, 18 c driven by electricity. The electric machines 17 a, 17 b canbe connected directly to the hydraulic pumps as well as connected to anelectric energy storage means 19, such as a battery or a supercapacitor, which in turn is connected to the hydraulic pumps. Theworking machine 1 preferably comprises such an electric energy storagemeans 19 for storing energy and providing energy to the hydraulic pumpsor to the electric machines 17 a, 17 b. Furthermore, conventionalcontrol units (not shown) can be used to control the energy transfer indifferent parts of the system illustrated in FIG. 4. As described inconnection to the FIGS. 1 and 2, the working machine 1 can have animplement 2 in the form of a bucket 3 which is operated by means of thehydraulic system 20. However, it should be emphasised that also otherimplements are naturally usable. When applying the invention on aworking machine such as an articulated hauler or a truck, the implementcan instead be for example a dump body. Usually a hydraulic pump andworking cylinders are used for the operation of the dump body during thedumping movement.

Preferably, the transmission line 110 comprises two electric machines 17a, 17 b, one 17 a of which is arranged upstream the transmission unit150 and the second 17 b is arranged downstream the transmission unit150. By using two electric machines the number of possible operationmodes is increased. In the embodiment illustrated in FIG. 4, thetransmission line comprises one first electric machine 17 a arrangedbetween the internal combustion engine 120 and the transmission unit150, and one second electric machine 17 b arranged between thetransmission unit 150 and the gearbox 140. The electric machines 17 a,17 b are electrically connected to each other for transmitting torquefrom the internal combustion engine 120 to the driving wheels 130 viathe first and second electric machines 17 a, 17 b. Furthermore, theelectric machines are electrically connected to the electric energystorage means 19 and to the respective motor 18 a, 18 b, 18 c of thehydraulic pumps. The first electric machine 17 a can be driven by theinternal combustion engine 120 for supplying energy directly to thehydraulic pumps or to the electric energy storage means 19, or to thesecond electric machine 17 b. The second electric machine 17 b can beused to brake the driving wheels 130 of the working machine 1 during abrake operation of the working machine and for supplying energy directlyto the hydraulic pumps or to the electric energy storage means 19. Thefirst electric machine 17 a or the second electric machine 17 b can alsobe powered by the electric energy storage means 19 in order to drive thedriving wheels 130 of the working machine 1, or the second electricmachine 17 b can be powered by the first electric machine 17 a for thesame reason.

Although, a transmission line 110 comprising two electric machines ispreferred, nevertheless advantages can be obtained by using one electricmachine only, preferably arranged between the transmission unit and thedriving wheels, and upstream any gearbox, i.e. between the transmissionunit and the gearbox in the same way as the second electric machine 17 bis arranged in FIG. 4. It is also possible to use one said electricmachine for each driving wheel. In such a case, usually four electricmachines are used for driving four driving wheels. Each electric machineis then preferably connected to the respective driving wheel via arespective gear box.

Furthermore, it would be possible to combine the prior art techniquewhere the hydraulic pump is driven by the internal combustion engine,for example such as described in connection with FIG. 3, with anelectric machine for driving the hydraulic pump. Then, the hydraulicpump can be driven by the internal combustion engine and/or the electricmachine at different times so as to optimize the operation.

In addition, the energy stored by the electric energy storage means 19may in some cases be used for other functions 61 of the wheel loader,such as compressors, fans, actuators, etc.

According to the method of the invention for operating a working machine1, at least one electric machine 17 a, 17 b comprised in thetransmission line 110 is used to drive or brake the driving wheels 130and/or generate electric power for said at least one hydraulic pump 100a, 100 b, 100 c. In addition to the advantages obtained by operating thehydraulic pumps by means of power from one or more electric machines 17a, 17 b, the electric machine 17 a, 17 b can be used for supplyingtorque to the driving wheels 130. By adapting the use of the internalcombustion engine 120 and/or the electric machine/machines 17 a, 17 b tothe current conditions, the total efficiency of the transmission line110 can be increased.

With reference to FIG. 4, the driving wheels 130 can be driven by:

The internal combustion engine 120 together with lock-up or torqueconverter 150, or the internal combustion engine 120 and/or the firstelectric machine 17 a and/or the second electric machine 17 b togetherwith lock-up or torque converter 150, or the first electric machine 17 aand the second electric machine 17 b without lock-up or torque converter150, or by the second electric machine 17 b without lock-up or torqueconverter 150.

The first electric machine 17 a can be driven by the internal combustionengine 120 for generating electricity or by the electric energy storagemeans 19 for providing torque, and the second electric machine 17 b canbe driven by the first electric machine 17 a or the electric energystorage means 19 for providing torque. The torque converter 150 could bereplaced by an ordinary hydraulic or mechanical clutch, offering thesame alternatives as for the lock-up state of the hydrodynamic torqueconverter.

It is further desirable that the invention is to provide a workingmachine comprising an electric power generating motor for supplyingelectricity to the working machine, the working machine furthercomprising at least one hydraulic pump in a hydraulic system for movingan implement arranged on the working machine and/or steering the workingmachine, which working machine enables a more effective operation of theworking machine and lower energy consumption.

By the provision of at least one electric machine for driving thedriving wheels of the working machine and a motor which supplies energyin the form of electricity, wherein the electric power generating motoris arranged to supply electricity to said at least one electric machineand said at least one hydraulic pump, the energy from the electric powergenerating motor, for example an internal combustion engine providedwith an generator, can be more efficiently used and the total energyconsumption can be lowered. The hydraulic system can be driven, withoutthe need of adapting the rotation speed of the electric power generatingmotor. Furthermore, the electric machine can be used as a brake during abraking operation of the working machine, such as a wheel loader, and atthe same time function as a generator for recuperating energy. Theenergy from the electric power generating motor can be directly suppliedto the electric machine and the hydraulic system or stored in anelectric energy storage means, such as a battery or super capacitor, tobe used later on.

Furthermore, the electric machine can be used for driving the drivingwheels in the reversed direction. This means that the reverse gear ofthe gearbox can be eliminated.

In FIG. 5 a working machine comprising an electric power generatingmotor 200 for supplying electricity to the working machine isillustrated. The working machine comprises at least one hydraulic pump100 a, 100 b, 100 c in a hydraulic system for moving an implementarranged on the working machine and/or steering the working machine. Theworking machine further comprises at least one electric machine 17 fordriving the driving wheels 130 of the working machine. The electricpower generating motor 200 is arranged to supply electricity to said atleast one electric machine 17 and said at least one hydraulic pump 100a, 100 b, 100 c.

Although the working machine illustrated in FIG. 5 has one electricmachine 17, it is possible to use two or more electric machines. Forexample, the working machine may comprise one said electric machine foreach driving wheel. In this case, usually four electric machines areused for driving four driving wheels. Each electric machine ispreferably connected to the respective driving wheel via a respectivegear box.

The working machine preferably comprises an electric energy storagemeans 19 for storing energy from the electric power generating motor 200and/or from said at least one electric machine 17. This electric energystorage means 19 is then used to provide electricity to said at leastone electric machine 17 and/or said at least one hydraulic pump 100 a,100 b, 100 c.

In addition to drive the driving wheels 130, one or more of said atleast one electric machine 17 can be used to brake the driving wheels ofthe working machine during a brake operation of the working machine. Atthe same time the electric machine 17 can function as a generator forrecuperating energy which energy can be stored in the electric energystorage means 19 and/or used for the hydraulic system 20.

In a preferred embodiment of the invention the working machine has atleast two implement and/or steering functions, and at least one saidhydraulic pump is arranged for each implement and/or steering function.In the embodiment examples schematically illustrated in FIGS. 2 and 5,the working machine comprises three hydraulic pumps 100 a, 100 b, 100 c;a first hydraulic pump 100 a is arranged to provide a lifting andlowering function of the implement, a second hydraulic pump 100 b isarranged to provide a tilting function of the implement, and a thirdhydraulic pump 100 c is arranged to provide the steering function of theworking machine. By separate hydraulic pumps for these functions theoperation of the working machine can be further optimized and thus thetotal energy consumption can be lowered.

Within the scope of the invention, the electric power generating motor200 can be 35 designed in many different ways as long as it is able toprovide electricity. One option is to use a fuel cell for providingelectricity. Another example of an electric power generating motor is aninternal combustion engine provided with an electric generator. Afurther solution is to use a gas turbine provided with an electricgenerator. The electric power generating motor can also be a free-pistonengine provided with an electric generator.

It should be pointed out that throughout the application the term“driving wheels” is meant to comprise vehicle wheels for directengagement with the ground as well as vehicle wheels for driving aground engaging member, such as tracks, crawlers or similar.

It is to be understood that the present invention is not limited to theembodiments described above and illustrated in the drawings; rather, theskilled person will recognize that many changes and modifications may bemade within the scope of the appended claims.

1. A working machine comprising an internal combustion engine forsupplying torque to driving wheels of the working machine, atransmission line arranged between the internal combustion engine andthe driving wheels for transmitting torque from the internal combustionengine to the driving wheels, at least one hydraulic pump in a hydraulicsystem for at least one of moving an implement arranged on the workingmachine and steering the working machine, wherein the transmission linecomprises at least one electric machine for at least one of driving thedriving wheels braking the driving wheels and generating electric powerfor the at least one hydraulic pump, wherein the transmission linecomprises a transmission unit for engagement and disengagement of theinternal combustion engine relative to the driving wheels, wherein thetransmission line comprises at least one electric machine arrangedbetween the transmission unit and the driving wheels and the at leastone electric machine arranged between the transmission unit and thedriving wheels is arranged between the transmission unit and a gearbox.2. A working machine according to claim 1, wherein the transmission linecomprises at least one other electric machine arranged between theinternal combustion engine and the transmission unit.
 3. A workingmachine according to claim 1, wherein the working machine comprises atleast one electric machine for each driving wheel.
 4. A working machineaccording to claim 3, wherein the transmission unit is a hydrodynamictorque converter.
 5. A working machine according to claim 4, wherein thehydrodynamic torque converter has a lock-up function where atransmission ratio of the torque converter is fixed.
 6. A workingmachine according to claim 1, wherein the transmission unit is amechanical clutch.
 7. A working machine according to claim 6, whereinthe hydrodynamic torque converter has a lock-up function where atransmission ratio of the torque converter is fixed, and wherein theworking machine comprises a plurality of electric machines, and at leasttwo of the electric machines are electrically connected to each otherfor transmitting torque from the internal combustion engine to thedriving wheels via the at least two electric machines.
 8. A workingmachine according to claim 1, wherein the working machine comprises anelectric energy storage means for providing energy to the at least onehydraulic pump.
 9. A working machine according to claim 1, wherein theworking machine comprises an electric energy storage means for providingenergy to one or more of the at least one electric machine.
 10. Aworking machine according to claim 8 wherein at least one of the atleast one electric machine is arranged to charge the electric energystorage means when the electric machine functions as a generator.
 11. Aworking machine according to claim 1, wherein at least one of the atleast one electric machine is arranged to brake the driving wheels ofthe working machine during a brake operation of the working machine. 12.A working machine according to claim 1, wherein at least one of the atleast one electric machine is arranged to drive the driving wheels ofthe working machine during operation of the implement or duringacceleration of the working machine.
 13. A working machine according toclaim 1, wherein at least one of the at least one electric machine isarranged to facilitate coupling or decoupling of a direct operationstate of the transmission unit by adapting the rotation of speed of theinternal combustion engine and the rotation of speed of the transmissionline to each other.
 14. A working machine according to claim 1, whereinthe working machine is a wheel loader.
 15. A working machine accordingto claim 1, wherein the working machine has at least two of at least oneof implement functions and steering functions, and at least one thehydraulic pump is arranged for each function.
 16. A working machineaccording to claim 15, wherein the working machine comprises threehydraulic pumps, a first hydraulic pump being arranged to provide alifting and lowering function of the implement, a second hydraulic pumpbeing arranged to provide a tilting function of the implement, and athird hydraulic pump being arranged to provide the steering function ofthe working machine.
 17. A method for operating a working machine havingan internal combustion engine for supplying torque to the driving wheelsof the working machine, and a transmission line arranged between theinternal combustion engine and the driving wheels for transmittingtorque from the internal combustion engine to the driving wheels, theworking machine further comprising at least one hydraulic pump in ahydraulic system for moving an implement arranged on the working machineand/or steering the working machine, comprising using at least oneelectric machine in the transmission line to at least one of drive thedriving wheels brake the driving wheels and generate electric power forthe at least one hydraulic pump, using a transmission unit in thetransmission line for engagement and disengagement of the internalcombustion engine relative to the driving wheels, using at least oneelectric machine arranged between the transmission unit and the drivingwheels and between the transmission unit and a gearbox and driving thedriving wheels by the electric machine, the electric machine beingelectrically powered by at least one other electric machine in thetransmission line and an electric energy storage means of the wheelloader.
 18. A method according to claim 17, comprising using the atleast one other electric machine arranged between the internalcombustion engine and the transmission unit, and driving the drivingwheels by the at least one other electric machine via the transmissionunit.
 19. A method according to claim 17 comprising driving the drivingwheels of the working machine by at least one of the at least oneelectric machine and the at least one other electric machine during atleast one of operation of the implement and acceleration of the workingmachine.
 20. A method according to claim 1, comprising using at leastone or mere of the at least one electric machine and the at least oneother electric machine for braking the driving wheels of the workingmachine during a brake operation of the working machine, and forrecuperation of energy during the brake operation.
 21. A methodaccording to claim 17, comprising driving the driving wheels while usinga hydrodynamic torque converter as a transmission unit.
 22. A methodaccording to claim 21, comprising driving the driving wheels during alock-up state of the hydrodynamic torque converter.
 23. A methodaccording to claim 17, comprising using at least one of the at least oneelectric machine and the at least one other electric machine for drivingthe driving wheels in a reversed direction relative to a direction ofrotation of the internal combustion engine.